High capacitance target structure for camera pick-up tube having dielectric sheet on metal mesh



Feb. 24, 1970 ajc. EINSTEIN 3,497,747

HIGH CAPACITANCE TAR G STRUCTURE I R CAMERA PICK-UP TUBE H NG DIE CSHEET ON ME MES Filed Aug. 1967 Z5 /9' A A9 /5 A9 /5 A9 /9 flea Z?Eff/M4306 f/A/STE/A/ INVENTOR ATTOZA/EV United States Patent 3,497,747HIGH CAPACITANCE TARGET STRUCTURE FOR CAMERA PICK-UP TUBE HAVINGDIELECTRIC SHEET 0N METAL MESH Bernard C. Einstein, Thousand Oaks,Califl, assignor to International Telephone and Telegraph Corporation, acorporafion of Delaware Filed Aug. 10, 1967, Ser. No. 659,776 Int. Cl.H01j 29/36, 31/50 US. Cl. 313-89 Claims ABSTRACT OF THE DISCLOSURE Atarget for a vidicon, or'thicon or other television camera-type tube isprovided having an evaporated layer of silicon monoxide or silicondioxide on a nickel or other conductive screen wire or electroformedmesh. The evaporated layer is thus perforate at the holes in the mesh. A1000 angstrom imperforate sheet of silicon monoxide or other dielectricis then fixed to the evaporated layer. The use of the thin sheet thusprovides a high sheet-to-mesh capacitance for high resolution and alarge dynamic range. However, the target is more rugged than is conventional because a molecular bond between the mesh and sheet increasesrigidity.

The invention herein described was made in the course of or of acontract or subcontract thereunder, with the US. Army.

Background of the invention This invention relates to the storage tubeart, and more particularly to a rugged storage tube target havingexceptionally good resolution and a wide dynamic range.

In the past it has been the practice to construct a storage tube targetby stretching a thin film or dielectric in a frame therefor. Supportedin this manner, the target is highly susceptible to damage through shockor vibration. Further, it is impossible to obtain good resolution and awide dynamic range with such a target because it is not possible to makethe film sufliciently thin for a large capacitance. This affects itscharging capacity and therefore its dynamic range. A large acceleratingvoltage is also required for the primary electrons and this, in turn,can cause poor resolution because of arcing or a distorted screenelectric field.

Summary of the invention In accordance with the device of the presentinvention, the above-described and other disadvantages of the prior artare overcome by providing a storage tube target including a metal meshhaving a perforate, evaporated layer of a first dielectric sandwichedbetween the mesh and a thin imperforate sheet of a second dielectric.The first dielectric is employed to provide a foundation bonded to themesh to which a uniform bond may be made with the sheet. Although theevaporated layer has holes therethrough in registration with those ofthe mesh, the sheet covers these holes.

By the use of the target of the invention it is possible to make thesheet as thin as 1000 or 650 angstroms. The sheet-to-mesh capacitance isthus very large and the target has a large charging capacity which makesits dynamic range large. That is, the size of the gray or half-toneregion of operation is increased. The large charging capacity also makesit possible to use What is known as a proximity focus. That is, aphotosensitive surface may be located very near the sheet with a verylow or zero primary electron accelerating voltage. The target may thusbe properly charged without any attendant arcing or ICC,

distortion due to high screen fields, and resolution is improved.

Still further, in accordance with the invention, a molecular bondbetween the evaporated layer and the mesh and sheet makes the entiretarget have a high integrity. It is therefore not severely damaged whensubjected to considerable vibration and shock.

The above described and other advantages of the present invention Willbe better understood from the following description when considered inconnection with the accom panying drawing.

Brief description of the drawing FIG. 1 is a side elevational view of atelevision cameratype tube partly in section;

FIG. 2 is a transverse sectional view greatly enlarged, of a storagetarget shown in FIG. 1.

Description of the preferred embodiments In the drawing in FIG. 1, astorage tube is indicated at 10 having a glass envelope 11. Aphotosensitive coating 12 is provided on the end of envelope 11. Astorage target is indicated at 13, and a collector grid is indicated at14.

As will be explained, tube 10 may be operated as a vidicon or as animage orthicon. In the case of vidicon operation, collector grid 14 mayor may not be omitted, as desired.

Tube 10 has an electron gun 15 for producing a scanning beam ofelectrons 16.

Tube 10 may be entirely conventional except for the construction andlocation of target 13.

Target 13 may be located sufficiently close to coating 12 so that asmall or zero accelerating voltage may be applied between coating 12 andtarget 13. In other Words, a proximity focus may be employed. This istrue because the charging capacity of target 13 is high. The manner inwhich such a high charging capacity is created is by the use of a verythin insulating sheet 17 shown in FIG. 2. Target 13 may include a metalmesh 18 made of a woven screen of circular wires 19. Alternatively, mesh18 may be an electroformed mesh having meshes of a square cross section.

In the construction of target 13, mesh 18 is supported in a conventionalclamp ring. It is stretched taut in the ring. A layer of siliconmonoxide 20 is then evaporated on one side of mesh 18'by use of anyconventional evap oration process. In lieu of silicon monoxide silicondioxide may be employed, if desired. The thickness of the dielectric at20 is not critical but is preferably at least one micron and not greaterthan 50 microns. Mesh-to-sheet capacitance decreases with increaseddielectric thickness. Structural strength and dielectric resistance toarcing and the like decrease with decreased dielectric thickness.

Sheet 17 is fixed to the dielectric at 20. The dielectric at 20 may bebonded to mesh 18. Sheet 17 may then be bonded to dielectric 20. Inother words, dielectric 20 may have a molecular bond with both. Further,if desired, sheet 17 may be additionally clamped to dielectric 20 byconventional clamp rings welded together as indicated at 21 and 22 inFIG. 2.

Mesh 18 and sheet 17 may be made from any one of several materials.Sheet 17 may also be fixed to dielectric 20 by any conventional method.For example, mesh 18 may be made of nickel, copper, silver or gold, orany alloy thereof. Sheet 17 may be made of silicon monoxide, silicondioxide, aluminum oxide, potassium chloride, sodium bromide, ormagnesium oxide.

Mesh 18 should be as fine as possible. It preferably has at least 500and preferably 1000 or 2000 or more lines per inch. However, the meshbecomes structurally weaker if it is finer than 2000 lines per inch.Sheet 17 preferably has a thickness of about 1000 angstroms. However,this thickness is not critical. For example, an electroformed sheet ofA1 of a thickness of 650 angstroms may be employed. The aluminum oxidesheet may be electroformed in the conventional way. In general, thealuminum oxide sheet will be supported on the surface of quantity ofwater. Mesh 18 will be supported below the waters surface in a pan withdielectric 20 on the upper side of the mesh. The water is drained outand the sheet 17 is then lowered onto dielectric 20 in a manner similarto that used in the prior art in preparing phosphor screens.

In an alternative embodiment, a drop of lacquer consisting essentiallyof any conventional nitrocellulose in a solvent is placed on top of thesurface of a quantity of water having an upper surface dimension of 12in. by 18 in. The film sets to a fairly hard state almost immediately.The water is then drained to allow the film'to deposit on dielectric 20as before. Silicon monoxide may then be evaporated on to the lacquerfilm by a conventional process. The target is then baked until thelacquer is evaporated. This will produce sheet 17 of silicon monoxidehaving a molecular bond to dielectric 20, which also may be made ofsilicon monoxide,

A typical woven nickel wire mesh of 1000 lines per inch supporting asilicon oxide layer 20 and an aluminum oxide sheet 17, exhibits goodresolution with a wide dynamic range with an accelerating voltagebetween coating 12 and target 13 of 100 to 500 volts. The mesh may haveinterstices of an area equal to one-half or considerably more thanone-half of the area of the mesh. When tube is operated in the vidiconmode, the video output of tube 10 is taken at mesh 18.

When tube 10 is operated in the orthicon mode, the video output is takenfrom collector 14.

It will be noted that electron beam 16 is directed toward target 13 onthe side thereof on which mesh 18 is bare. Primary electrons fromcoating 12 are directed against the surface of sheet 17 opposite thesurface thereof which lies in contact With dielectric 20.

In accordance with the foregoing, it is possible to construct target 13with a dielectric sheet 17 of an extremely small thickness, Thecapacitance between the surface of sheet 17 which is charged by theprimary electrons and mesh 18 is therefore very large. This permits theuse of said proximity focus and a low zero primary accelerating voltage.This, in turn, prevents arcing and electric field distortion in thetarget 13 for a highly reliable resolution.

The high capacitance also increases the dynamic range of the target 13.

Still further, in spite of the fact that sheet 17 is very thin, target13 has considerable structural integrity because of the proximity ofsheet 17 to dielectric 20 and mesh 18, and the molecular bondstherebetween. A clamping device can also act as an additional orindependent brace.

Although only a few specific embodiments of the invention have beendescribed in detail, many changes and modifications will suggestthemselves to those skilled in the art. The invention will therefore notbe limited to the specific embodiments selected for this disclosure, thetrue scope of the invention being defined only in the appended claims.

What is claimed is:

1. A storage tube target comprising: a conductive wire mesh; a firstdielectric evaporated on one side of said mesh having holes therethroughin registration with the holes in said mesh; and an imperforate sheet ofa second dielectric bonded to said first dielectric in a positioncovering said registering holes.

2. The invention as defined in claim 1, wherein said first dielectric isa perforate evaporated layer of silicon monoxide having a maximumthickness of at least one and not more than fifty microns, said layerbeing bonded to both said mesh and said sheet.

3. The invention as defined in claim 2, wherein said sheet is anelectroformed layer of aluminum oxide having a molecular bond to saidevaporated layer, said sheet having a thickness of about 0 angstroms.

4. The invention as defined in claim 2, wherein said sheet is anevaporated layer of silicon monoxide, said sheet having a thickness ofabout angstroms.

5. The inventionas defined in claim 2, wherein said mesh has at least500 wires per inch, said wires being circular in cross section.

6. The invention as defined in claim 2, wherein said sheetis made ofpotassium chloride.

7. The invention as defined in claim 2, wherein said sheet is made ofmagnesium oxide.

'8. The invention as defined in claim 2, wherein said sheet is made ofsodium bromide.

9. The invention as defined in claim 2, wherein said mesh is made ofnickel and has 1000 lines per inch.

10. The invention as defined in claim 1, wherein said first dielectricis a layer of silicon dioxide havng a maximum thickness of at least oneand not more than fifty microns,

References Cited UNITED STATES PATENTS 2,237,681 4/1941 McGee et a1117-2l0 X 2,579,772 12/1951 Wilder 117210' 2,713,648 7/1955 Gardner31367 X 2,922,906 1/1960 Day et a1. 313-65 3,179,834 4/1965 Ochs 313893,408,531 10/1968 Goetze et al. 3l389 X JAMES W. LAWRENCE, PrimaryExaminer V. LA FRANCHI, Assistant Examiner US. Cl. X.R. 250213; 313-348

